1. Field of the Invention
The invention relates to a method of machining a motion-supporting surface of a cylinder of an internal combustion engine. In particular, the invention relates to a method of coating the motion-supporting surface where the latter is roughened beforehand to improve the adhesion of the coating.
2. Description of Related Art
For reasons of weight, internal combustion engines in motor vehicles are often formed to have a cylinder block and crankcase of light metal, and in particular of aluminum. However, something which is problematic in this connection is that, because of the tribological properties of the light metal, and in particular its comparatively poor resistance to wear, the inner walls of the cylinders formed in the cylinder block and crankcase are only inadequate in respect of their suitability as motion-supporting surfaces for the pistons.
To avoid this problem, cylinder liners of, for example, grey cast iron are used in many internal combustion engines having a cylinder block and crankcase of light metal, whereby the advantages of the light metal (low specific weight) can be combined with those of grey cast iron (good tribological properties).
As an alternative to this, it is known for the motion-supporting surfaces of the light metal cylinder block and crankcase to be provided with a coating in order to produce the desired tribological properties for the motion-supporting surfaces. The coating is regularly produced in this case by melting the coating material and spraying it onto the cylinder walls.
Something which is of particular importance when cylinder walls are being coated is to produce good adhesion of the coating to the substrate material. For this purpose, it is known for the motion-supporting surfaces of the cylinder block and crankcase to be roughened before being coated, in order to increase the surface area for contact between the layers. An attempt is often also made in this case to create in the roughened motion-supporting surface undercuts into which the melted material of the coating can penetrate in order to produce, after solidification, a positive connection between the layers.
One known possible way of roughening the cylinder walls is to introduce grooves or channels by stock-removing or non-stock-removing processes.
In this way, it is known from, for example, DE 10 2009 027 200 B3 for a spiral groove of, in particular, rectangular or trapezoidal cross-section to be introduced into a cylinder wall in the first step of a method of roughening the cylinder wall. This can be done by both stock-removing and non-stock-removing processes. In a second step, the land which extends in a spiral form between the grooves is then plastically deformed in the radial direction, section by section, to create undercuts. What is used to introduce the groove is a tool which has a single cutting edge, the tool both being driven in rotation and also being displaced axially along the longitudinal axis of the cylinder.
A similar method is known from EP 2 112 359 A1. What is also disclosed in that case is a plurality of grooves extending in the circumferential direction being introduced into the cylinder wall rather than one spiral groove.
Disadvantages of the known methods are the considerable amount of time taken to introduce the grooves and the comparatively short life between dressings of the tools used to do so.